I am using a Linux computer with bluez version 4.101. I am communicating with a BLE device in slave mode. I am trying to read data from the BLE device. But when I do that th
Try using --sec-level=medium
or --sec-level=high
with gatttool. I'm not sure how those work, but essentially you don't have the right level of security to read that attribute. Pairing ups your security level, and that's why it works on your iPhone.
You may also want to try -I
for an interactive prompt with gatttool.